How do I calculate my tranny gear ratio on a belt drive car?
A2. On a belt drive system, the gear that is in your differential is usually the bigger of the two and is called the spur gear. The pulley gears are usually where near where you mount your motor and those are your pinion gears. So take the pinion gear and divide it into your spur gear which gives the tranny ratio of your car. Example: I have an electric Colt10 which is belt drive. The pulley/pinion gears have 15t and the diff/spur gears have 35t. The math would look like this – 35 / 15 = 2.33. So my tranny ratio for my car is 2.33:1. Now use this along with the math in question # 1 to get your final drive ratio.